[r6rs-discuss] Date and time arithmetic library proposal for R7RS large Scheme
cowan at mercury.ccil.org
Fri Nov 26 20:38:56 EST 2010
r6rsguy at free-comp-shop.com scripsit:
> > In any case, most computer clocks aren't accurate to
> > 1 part in 10^8, which is the discrepancy between
> > Posix time and UTC time since the beginning of UTC.
> How many milliseconds is that?
It's 24,000 ms out of the last 39 years, or approximately
1,230,720,117,120 ms. That is one part in 0.00000002.
> I am not worried about precision, I am worried about correct arithmetic.
I agree that subtracting one value of current-posix-millisecond from
another has a rather small empirical probability of being off by 1000 ms,
namely 1 in 10^-8. I have added a note to TimeCowan saying so.
Note that 1 ms resolution does not necessarily imply 1 ms precision: in
most Java implementations, you get 1 ms resolution but only 1 s precision.
As for accuracy, typical computers with access to the Internet can be
made accurate to about 35 ms, if carefully watched.
> You are *forbidding* an implementation to increment the clock before
> a leap second?
Yes, absolutely. UTC time is readily available (except during leap
seconds), TAI time is not.
John Cowan cowan at ccil.org http://ccil.org/~cowan
No man is an island, entire of itself; every man is a piece of the
continent, a part of the main. If a clod be washed away by the sea,
Europe is the less, as well as if a promontory were, as well as if a
manor of thy friends or of thine own were: any man's death diminishes me,
because I am involved in mankind, and therefore never send to know for
whom the bell tolls; it tolls for thee. --John Donne
More information about the r6rs-discuss